A new method for casting discrepancy: some results for a phosphate-bonded investment.
OBJECTIVE
An accurate and realistic casting discrepancy method applicable to base metal alloys has hitherto been lacking. The purpose of this study was to develop a method for determining casting discrepancy free of interference from oxide, slag and surface defects, working under realistic conditions. In addition, a variable was sought that could be used for calibrating the casting process to allow for local errors.


METHODS
A crown pattern was designed to incorporate circular V-grooves on the margin and the inside surface of the occlusal part for determination of the 'groove root diameter' (GRD) with a measuring microscope. Castings using a phosphate-bonded investment were made to test the effects of 'hygroscopic' expansion, burn-out temperature, powder/liquid ratio and groove location.


RESULTS
The tested investment variables showed the expected effects, but the distortion between marginal and pulpal regions was clearly shown, as were interactions between some variables. 'Special liquid' proportion appears to be a good candidate variable for process calibration.


CONCLUSIONS
The GRD method was shown to be sensitive and reproducible. It is also applicable to many other casting systems, and in particular to monitoring overall process discrepancy, i.e. from tooth preparation to casting, which is suggested as being the key issue.
Ho
E K
EK
Dental Technology Unit, University of Hong Kong, Prince Philip Dental Hospital, Hong Kong.
Darvell
B W
BW
D000704:Analysis of Variance; D002138:Calibration; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003442:Crowns; D003722:Dental Alloys / Q000737:chemistry*; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique / Q000145:classification; D017267:Dental Prosthesis Design; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D008853:Microscopy; D010087:Oxides / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry*; D011208:Powders; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012996:Solutions; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic; D014867:Water / Q000737:chemistry
D003722:Dental Alloys; D003734:Dental Casting Investment; D010087:Oxides; D010710:Phosphates; D011208:Powders; D012996:Solutions; D014867:Water